In Commonly assigned U.S. Pat. Nos. 4,933,780, 4,977,419, 5,006,873, 5,025,283, and 5,276,472, a photographic filmstrip having a virtually transparent, magnetic film layer covering the non-emulsion side of the filmstrip (referred to as an MOF layer) is disclosed in conjunction with various camera systems. Potential longitudinal recording tracks are illustrated in the MOF layer in both the image frame area and on either side of the image frame area for recording information such as film type, film speed, film exposure information and information relevant to the processing and subsequent use (e.g., printing) of the exposed image frames. The systems disclosed therein provide for recording of information during film manufacture, reading and/or recording of information on certain tracks during camera use, and reading and/or recording of printer related information during photofinishing. The information recorded during camera use may include voiced messages or sound associated with the photographed scene and may be recorded in digital or analog format on certain of the tracks.
The specific camera recording tracks and recording heads disclosed in the `419 and `780 patents are disposed to record in tracks located along the longitudinal edges of the film and outside the MOF layer in the image frame area. Further commonly assigned U.S. Pat. Nos. 5,034,836, 5,041,933, 5,274,522 and 5,285,324 and U.S. Pat. No. 5,307,100 disclose magnetic recording head configurations for use in recording in longitudinal tracks alongside the filmstrip edges but not in the image frame area.
The above-referenced patents showing magnetic recording heads along the edges of the filmstrip outside the image area generally teach providing pressure pad supports or rollers on the emulsion side opposite from the recording heads and continuous motion of the recording medium to ensure reliable recording. In the above-referenced `100 and `324 patents, various configurations for mounting a magnetic recording head in relation to the film transport path and film plane with the use of an oppositely disposed pressure rollers are disclosed in a camera.
In the above-referenced `780 patent, a different approach is taken wherein the recording head of the camera is positioned with respect to the chamber for receiving a modified film cartridge. The recording head bears against the MOF layer of a filmstrip exposed through an opening in the film cartridge lip. The film is supported and flattened within the lip, and the emulsion bears against a compliant support formed with a light blocking plush material overlying a lower flange of the cartridge lip.
The `780 patent also suggests that an elongated array of recording heads may be positioned to penetrate an elongated opening in the cartridge lip, relying on the plush as a backing support. The approach taken in the `780 patent requires the acceptance of a new film cartridge standard in the industry, and the use of plush material to block light entry through the opening.
None of the above-referenced patents specifically disclose magnetic recording head arrays (i.e., multi-head arrays) or any specific support structures for each magnetic recording head element for recording or reproducing in a plurality of tracks in the MOF layer on the side of the film opposite to the image frame area or support structures. Reading and recording information on tracks of a magnetic coating or stripes of magnetic coatings in the image frame area on photographic film in a still camera require solutions to problems different than those encountered in other magnetic media recording apparatus.
In a disk drive, the recording head flies or floats on the air film that is created as the nominally flat surface of the magnetic disk rotates at high speed on an actuator assembly as shown in U.S. Pat. No. 5,282,102, for example. The disk is not inherently curved or irregular as it rotates, and close recording head compliance can be attained. Pitch and roll of the magnetic recording head to follow minute irregularities in the magnetic disk surface is allowed by the configuration of the mount at the free end of the loading arm of the actuator assembly.
In a tape drive, the magnetic tape is flexible enough under tension to conform to the recording head contour both in the tape feed direction and in the cross-tape direction. Magnetic tape is quite thin and exhibits virtually no stiffness. And recording is done with the magnetic tape moving at a constant speed.
Photographic film, however, is of much greater thickness than the magnetic tape used for commercial and consumer recording and reproduction and is neither compliant nor inherently flat. When removed from its cartridge, a filmstrip shows a relatively high stiffness and very observable cross-curvature across its width that is convex on the non-emulsion side of the film. Further, the unwrapped filmstrip also shows a convex curvature along its length, again on the non-emulsion side of the film. This latter curvature is attributed primarily to a core-set curl that results from the filmstrip having been tightly wound on a film cartridge spool.
The cross-film curvature across the width of the filmstrip is primarily caused by the number of multilayers of emulsion and MOF layer (if present). The emulsion multilayers (and MOF layer, if present) have different stretch properties than that of the base film substrate of acetate, PET, or PEN material. The cross-Curvature is also influenced by the bending phenomena known as anticlastic curvature. The degree of filmstrip cross-curvature also depends on environmental conditions, including the time and temperature history of the film, the relative humidity, and the thickness of the film. Because of the cross-film curvature, it is difficult to achieve good contact or compliance across the width of a wide, multi-head array. To provide a reliable read or write signal, the magnetic recording head must remain in close proximity to the magnetic coating. Any disturbances, such as variations in film curl, can vary the relationship of the recording head to the magnetic coating and decrease the reliability of the signal.
The space limitations in a portable hand held still camera, which necessarily must be as compact and light as possible to appeal to the average consumer, restrain the size and location of the magnetic recording head and the film drive system. In the cameras described in the above-referenced patents, the information is intended to be recorded in the MOF layer in the longitudinal tracks (defined by recording head spacing positions across the filmstrip) along the edge of or across the image area opposite to the exposed image frame, so that this information can be recombined with the image, even if the negatives are subsequently separated into individual image frames. Because of this requirement, the magnetic recording must take place downstream of the camera exposure gate area while the filmstrip is advanced to the next exposure. The exposure gate region in the camera where images are exposed is designed with film rails and a backing plate to confine and control the photographic filmstrip curvature to ensure that objects are optimally and uniformly focused by the camera lens across a given frame. The planarity of the film in other areas within the camera, specifically the downstream area, is not as carefully controlled. Thus, the filmstrip is susceptible to a greater degree of non-planarity associated with spooling, film cross-curvature, edge conditions, and other plastic deformations resulting from time, humidity, and temperature exposure described above.
The film motion during recording takes place in a frame stepping mode by means of a pulse of tension (i.e., jerking or jogging motion). When the pulse of tension is applied to a stationary filmstrip, the film tension conditions at the recording head/MOF layer interface are highly variable compounding the problems associated with the non-planarity and noncompliance of the filmstrip.
Of particular importance, the recording head-to-film interface must avoid scratching the MOF layer or the emulsion layers or the image quality will be degraded. The above-referenced patents related to the MOF layer on the filmstrip that show recording head structure are largely silent as to how to overcome these problems with recording in the image frame area.
The magnetic recording process requires that a recording head gap be in close proximity or contact with the magnetic media. Wide or non-uniform spacing separations between the recording head gap and the MOF layer result in lower recording density or a degraded signal. Maintaining a uniform contact or spacing of the recording head gaps with the MOF layer, without distorting the natural filmstrip curvature or the flatness of the filmstrip achieved in the exposure gate, is a challenge due to the films' non-planar nature and stiffness as described above.